Trying to tell the life story of any individual within the confines of a normal feature film is a difficult task–unless your subject is Pauly Shore, it is almost impossible to tell a complete story in around two hours without dropping or reshaping a lot of significant material in the process. It becomes even more difficult when the subject is famous enough so that most viewers have a pretty good idea of what the person in question looks, sounds and acts like–the performer has to figure out a way to play them so that it feels like a real performance and not simply an extended impersonation. The makers of “Walk the Line” have an additional hurdle to face in addition to those–their subject is Johnny Cash, a man who based his entire career on never sounding less than 100% authentic whenever he sang, even when crooning a ditty along the lines of “A Boy Named Sue.” For him, a standard-issue glitzy Hollywood version of his story wouldn’t do–it just wouldn’t feel right and the film would be doomed from the start. Luckily, “Walk the Line,” while it doesn’t exactly reinvent the musical biopic, has that sense of authenticity about it and the result is one of the better examples of the genre–one aided in no small part by the efforts of stars Joaquin Phoenix and Reese Witherspoon, who, as Cash and June Carter, turn in two of the very best performances of the year

Although the details may be different, the broad outlines of Cash’s story, as told here, will not come as a surprise to students of the genre. We glimpse a childhood marred by tragedy (his older brother perished in a tragic accident with a power saw) and a strained relationship with a parent (his father, played here by Robert Patrick.) We see Cash as he struggles to provide for wife Vivian (Ginnifer Goodwin) and his family while doggedly pursuing his dream of being a musician, including a view of him penning the lyrics to what would eventually become “Folsom Prison Blues.” There is the scene in which he auditions for the legendary Sam Phillips at Sun Records and gradually begins to develop the sound that would make him famous. There are the early heady days of fame and fortune that see him running from gig to gig with the likes of Elvis Presley (who offers him pills and chili fries), Jerry Lee Lewis (who preaches hellfire) and Roy Orbison (who just sings his heart out night after night). There are struggles with drugs, groupies and a wife who would prefer a husband who she could see at home instead of a star appearing on magazine covers. There are the low points in which Cash’s demons get the better of him and he is on the edge of losing everything and, of course, the eventual triumph in which he puts those demons behind him and stops taking his gifts for granted.

This is the kind of stuff that you have seen many times before–adjust a few of the details and the above description could easily fit last year’s “Ray.” The key element that separate “Walk the Line” from other such films is the relationship that develops between Johnny and June. As a child, we see Johnny smitten with June’s voice on the radio and when he meets her in person for the first time (a backstage accident that the more seasoned June turns into a crowd-pleasing bit), he is thunderstruck by her beauty and stage presence. Later that evening, in a dingy diner, he chats her up again and finds her just as compelling off the stage. For him, this is a love as pure and true as the kind he sings about and it both maddens and delights him that she has been around the block enough to know that to take up with a fellow tour member–especially one who is married–is bad news. And while she resists, even she knows that they are great together on stage and continues to work with him. For one moment, she even convinces herself to take their relationship to the next level but when she realizes the extent of his pill habit, she breaks her ties to him. And yet, when he hits rock-bottom, it is June who pulls him back together and inspires him to create some of the most memorable music recorded in the 20th century.

The gamble on focusing the majority of the film on the Johnny-June relationship (it ends with their 1968 marriage with title cards filling in the rest) pays off wonderfully here because of the performances of Phoenix and Witherspoon. For Phoenix, who has developed into one of the more intriguing young actors working today with such films as “To Die For,” “Gladiator,” “Quills” and “Buffalo Soldiers,” the part of Cash makes for an excellent use of his brooding intensity–like Jamie Foxx in “Ray,” his work goes far beyond mere impersonation to the point where he simply turns into Johnny Cash before our eyes–and it is by far the best work he has done to date. For Witherspoon, the brilliant actress who has lately been squandering the talent that she displayed in “Election” on a series of increasingly irrelevant you-go-girl epics that have pleased studio accountants and few others, her performance is a blessed return to form. Her June Carter is just as tough, funny and feisty as Johnny Cash but there is a vulnerability to her as well that Witherspoon deploys at key moments that has a devastating impact. It should also be noted both Phoenix and Witherspoon–neither of whom are singers by trade–do all of their own singing here and tear into such tunes as “Jackson,” “I Walk the Line,” “It Ain’t Me, Babe” and “Ring of Fire” with such energy and joyous abandon that you will be forgiven for thinking that you are hearing the real Cash and Carter on the soundtrack.

The film was directed by James Mangold, whose filmography is one of the more curiously schizoid around. When he is working on something that clearly engages him–such as “Heavy” (1995) or “”Copland” (1997), he is a director with a facility for both detailing the details of authentic everyday life and with handling actors. When he isn’t–take such nonsense as “Kate and Leopold” (2001) or the abysmal “Identity” (2003)–he can be the biggest hack around. Thankfully, “Walk the Line” is a demonstration of the former Mangold at the top of his form. He has a firm feel for the details of Cash’s life–both the highs (such as the sweaty nights on stage where the music is played with such ferocity that he feels on top of the world) and the lows (when he is reduced to swallowing handfuls of pills to get the same feeling that he once achieved with a couple of guitar chords)–without letting things fall too far into cliche. His screenplay, co-written with Gill Dennis, does a good job of stripping the story to the basics and his direction keeps things moving along at a steady pace that never lets things drag.

“Walk the Line” isn’t flawless. The character of Vivian Cash (a strong turn by Goodwin) disappears from the proceedings about two-thirds of the way through and it feels as if something is missing. Also, the focus on June’s refusal to marry Johnny during the final stretch is drawn out a little too long for its own good–after all they have gone through at that point, her refusal seems more than a little churlish. However, these are minor quibbles because the film has so much more going for it than against it. Some viewers may feel compelled, as I have in this review, to compare the film to “Ray.” To these eyes, it is no contest. “Ray” had one stunning performance and not much else going for it. “Walk the Line,” on the other hand, doubles the number of stunning performances and throws so much more in for good measure and the result is the rare biopic that is actually worthy of its subject.